Different types of hidden hinges are known, but they have several drawbacks.
With reference for example to the hinge described in EP1612356, it does not allow opening of the sash by more than 100-110 degrees (relative obviously to the fixed frame). The same drawback is associated with the hinge described in EP1918498. The limited opening range of the sash constitutes a not minor problem for the manufacturer who, in order to prevent the sash in the fully open position from accidentally closing for example under the action of the wind, must mount an additional stop arm. This results, as may be easily imagined, in considerable complication of the constructional design of the window as well as increased manufacturing costs.
Also known are hinges which allow opening of the sash through 180 degrees with respect to the fixed frame. This is the case for example of the hinges described in the two European patent applications EP2708692 and EP2703587. However, these hinges are constructionally complex and therefore subject to malfunctions and breakages. Moreover they are difficult to assemble and involve not insignificant manufacturing costs.
The hinges described above have a further drawback due to the fact that sliding connections are provided in them. This results in greater friction and therefore more rapid wear, on the one hand, and the need to apply a greater operating force, on the other hand.
Furthermore, the hinges described above do not allow adjustment of the pressure in the direction parallel to the plane of the window itself, namely adjustment of the closing pressure of the perimetral seal of the window.
A further example of the hidden hinge is that described in the publication EP2811092. This hinge allows opening of the sash by up to 180°. However, this hinge is particularly bulky in the direction of the thickness of the window. This bulkiness is considerable and prevents such a hinge from being used on profiles of small-thickness or thin windows such as those which are currently widely used.